About the finale (this doesn't actually contain spoilers of any significance, but I'm putting it in spoiler tags anyway, in case you don't want to read anything at all about the finale, not even opinions.)
I think the finale was quite ok, even though I thought it was a bit of a letdown given the grandiose nature of the previous two season finales, where they went really the extra mile to make them spectacular and epic. There was kind of an attempt at this in the setup, but ultimately in the end it just felt like a somewhat average mid-season episode.
Although, in some sense, that was also somewhat of a relief. At one point I was actually fearing they would pull another Magical Mystery Cure and actually make Starlight Glimmer a princess. I was thinking "no, no, no, please don't, no, no, don't do that, please oh please. Don't make another MMM, please." Luckily, they didn't, and I'm really relieved because of that.
I really liked the idea of making, not just a regular episode, but the season finale of all things, it about secondary characters (nice lampshade hanging from you-know-who, too.) It was a refreshing change of pace. Too bad that the finale turned out to be, regardless of the promising beginning, rather meh and average.
I think there was a great missed opportunity in the first half, where they could have prolonged the "mystery" longer, ie. the strange behavior of the ponies when Starlight returns to Ponyville. They could have eg. made it look like nobody remembers her and that eg. apparently something has happened to the timeline, or something. But they disposed of any such possible plotlines way too quickly, which was a shame.
Also, the radical change in the end happened way, way too easily. I know, kids' show, limited runtime, but still... way too easily. Broke willing suspension of disbelief.